It is possible to update TestNG via RH Central.

1. RH Central -> Software/Update
2. Enable Early Access
3. Show installed
4. Find "TestNG" there is written "Installed, update available"
5. Select TestNG and install updates
6. Restart
7. Then this error message will appear in the log:

!ENTRY org.testng.eclipse 4 0 2017-04-21 05:21:07.715
!MESSAGE FrameworkEvent ERROR
!STACK 0
org.osgi.framework.BundleException: Could not resolve module: org.testng.eclipse [1649]
  Another singleton bundle selected: osgi.identity; osgi.identity="org.testng.eclipse"; type="osgi.bundle"; version:Version="6.11.0.201703011520"; singleton:="true"

Log: https://dev-platform-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/view/Devstudio/view/devstudio_rpm_tests/job/rpm_rh_central_test.weekly/57/artifact/devstudio-rpm-central.test/eclipse_log/rh-eclipse46-devstudio-10.4-0.20170421.0123.el7_20170421-0519_install_TestNG.txt

Central constains org.testng.eclipse 6.11.0.201703011520, RPM contains 6.9.13.201701201452.